Lubricating composition having improved thermal stability



United States Patent 3,268,445 LUBRICATING COMPOSITION HAVING IMPROVEDTHERMAL STABILITY Henry A. Ambrose, Penn Township, Allegheny County, andPaul R. McCarthy, Allison Park, Pa., assignors to Gulf Research &Development Company, Pittsburgh, Pa., a corporation of Delaware NoDrawing. Filed Dec. 14, 1962, Ser. No. 244,602 3 Claims. (Cl. 252--25)This invention relates to an improved lubricating composition and moreparticularly to a lubricant suitable for use at high and ambienttemperatures.

The trend in design of modern aircraft has accentuated the need forlubricants which will lubricate anti-friction bearings operating at highrotational speeds and high temperatures. Considerable progress has beenmade in recent years in producing improved aircraft lubricants. Forexample, a number of lubricants are now available for lubricatingbearings operating at 10,000 to 20,000 revolutions per minute attemperatures up to about 400 F. However, great difliculty has beenencountered in producing a lubricant which will effectively lubricatebearings operating at speeds up to 20,000 revolutions per minute and attemperatures up to about 600 F. for prolonged periods of time.

In order to produce a lubricant, whether a liquid or a compositionhaving the consistency of a grease, which will effectively lubricatebearings operating at temperatures up to 600 F. it is necessary toemploy as the fluid component a material which is highly resistant tothermal degradation at temperatures up to 600 F. In addition, the fluidcomponent must have the ability to lubricate and remain fluid both athigh and ambient temperatures over a prolonged period of time withoutexcessive volatilization, gumming or coking. If a composition having theconsistency of a grease is prepared, the thickening agent employed inconjunction with the fluid must remain solid and also be resistant tothermal degradation at temperatures up to 600 F.

While some mineral oils especially hydrotreated mineral oils aresufliciently stable to provide adequate lubrication when used undermoderately elevated temperatures, the volatility of mineral oils is suchthat they do not give adequate lubrication at temperatures in the orderof 600 F. Synthetic oils are substantially more resistant to thermaldegradation than mineral oils. Synthetic oils, particularly thepolyorgano siloxanes known as the silicone oils in addition to beingmore resistant to thermal degradation than mineral oils also have highviscosity indices making their use at high and ambient temperaturesespecially desirable. Notwithstanding these desirable characteristics,the synthetic oils are also prone both to volatilization andsolidification when heated at 600 .F. over prolonged periods.

We have found that the thermal stability of a synthetic oil particularlypolyaryl ethers can be enhanced by adding thereto an alkaline earthmetal hydroxide.

Exemplary of the polyaryl ethers which are improved according to theinvention are the liquid polyphenyl ethers, i.e.,m-bis(m-phenoxyphenoxy)benezene and mbis(m-phenoxyphenoxy) phenyl ether.

The alkaline earth metal hydroxides which are employed according to theinvention can be either chemically pure or commercial grades thereof.The hydroxides of the metals calcium, barium, strontium and magnesiumcan be powdered or finely divided such as colloidal calcium hydroxide,colloidal barium hydroxide, colloidal strontium hydroxide and colloidalmagnesium hydroxide. Of these compounds, calcium hydroxide is especiallypreferred in preparing lubricating compositions of the invention. Theamount of the alkaline earth metal compound which we use may varydepending upon the particular lubricating base employed and upon thecharacteristics desired in the ultimate composition. In improving asynthetic oil, a suflicient amount of the alkaline earth metal compoundis used to improve the thermal stability of the oil. In general, theamount of the alkaline earth metal compound employed, is about 0.1 toabout 3 percent by weight based on the weight of the total composition.

The lubricating composition of this invention can con tain conventionallubricant additives, if desired, to improve other specific properties ofthe lubricant without departing from the scope of the invention. Thus,the lubricating composition can contain a filler, a corrosion and rustinhibitor, an extreme pressure agent, an antioxidant, a metaldeactivator, a dye and the like. Whether or not such additives areemployed and the amounts thereof depend to a large extent upon theseverity of the conditions to which the composition is subjected andupon the stability of the synthetic lubricating oil base in the firstinstance. When such conventional additives are used they are generallyadded in amounts between about 0.01 and 5 percent by weight based on theweight of the total composition.

In order to compare the improvement obtained upon the addition of analkaline earth metal hydroxide to a polyorgano siloxane containingdiphenylmethylsilyl end groups (QF67024) and to a liquid polyphenylether, m-bis(m-phenoxyphenoxy)benzene, viscosities of each were examinedboth before and after heating at 600 for extended periods. The resultsobtained are summa rized by the data in Table I. Inasmuch as theuncompounded oils become quite viscous after heating to 600 F. for 96hours or more, the reported values for these viscous materials areconsidered to be approximate values but nevertheless are comparativewith each other since the viscosities were obtained by identicalprocedures.

TABLE I Viscosity, SUS at F. Alter Indicated Hours at 600 F.Composition, percent By Weight The strikingly improved thermal stabilityof the polyphenyl ether composition of the invention containing 1percent by weight of calcium hydroxide is self-evident from the abovedata. It will be noted that whereas the calcium hydroxide did not changethe initial viscosity of the lubricating oil, the calcium hydroxideeffectively reduced the amount of viscosity increase when thecomposition was heated to 600 F.

While our invention has been described with reference to variousspecific examples and embodiments it will be understood that theinvention is not limited to such examples and embodiments and may bevariously practiced within the scope of the claims hereinafter made.

Patented August 23, 1966 We claim:

1. A lubricating composition capable of functioning at temperatures upto about 600 F. consisting essentially of a dispersion in a liquidpolyphenyl ether of a small amount, sufiicient to improve the thermalstability of said ether, of an alkaline earth metal hydroxide.

2. A lubricating composition capable of functioning at temperatures upto about 600 F. consisting essentially of a dispersion in a liquid,polyphenylether of aboutOul .to

about 3 percent by weight of calcium hydroxide.

3. The lubricating composition ofclaim 2 wherein the polyphenyl ether ism-bis(m-phenoxyphenoxy) benzene.

References Cited by the Examiner UNITED STATES PATENTS Vinograd et .al.25225 Lindstrom et al. 25225 Zajac 25225 Peterson 25225 Peterson et a1252--25 Halter et a1. 2525 1.5

10 DANIEL E. WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner.

1. A LUBRICATING COMPOSITION CABLE OF FUNCTIONING AT TEMPERATURES UP TOABOKOUT 600*F. CONSISTING ESSENTIALLY OF A DISPERSION IN A LIQUIDPOLYPHENYL ETHER OF A SMALL AMOUNT, SUFFICIENT TO IMPROVE THE THERMALSTABILITY OF SAID ETHER, OF AN ALKALINE EARTH METAL HYDROXIDE.